I hope having an 'external' site for the app submission would not cause confusion/problems. The easiest way for a user to test an app is to install it (through the app manager). So the idea of an .install file uploaded on the site that linking to the extras-devel/testing should be a must, otherwise, regarding for the dependencies, the user could fall into problems and stop testing apps for the competition. So, IMHO all the apps for the competition need to be uploaded to the extras repository.